Fix NIIT calculations

[martinholmer]

This pull request make some slight changes in the calculation of the Net Investment Income Tax (NIIT), which was introduced beginning in 2013. These changes have tiny effects on Tax-Calculator results. For example, the aggregate income tax liability over the 2013-2022 period declines each year by an amount that ranges from $0.1 to $0.3 billion, which is at most only about 0.02 percent of tax liability.

The most pervasive changes are in the Internet-TAXSIM validation results, which are now off a little bit because it would seem that Internet-TAXSIM contains the same bugs as are fixed in this pull request.

This pull request resolves issue #873, which contains a more extensive discussion of the code changes in this pull request.

@MattHJensen @feenberg @Amy-Xu @GoFroggyRun @zrisher @codykallen

[codecov-io]

Current coverage is 98.12% (diff: 100%)

Merging #874 into master will not change coverage

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[feenberg]

We will fix Internet Taxsim this afternoon.

dan

On Wed, 24 Aug 2016, Martin Holmer wrote:

This pull request make some slight changes in the calculation of the Net Investment
Income Tax (NIIT), which was introduced beginning in 2013. These changes have tiny
effects on Tax-Calculator results. For example, the aggregate income tax liability
over the 2013-2022 period declines each year by an amount that ranges from $0.1 to
$0.3 billion, which is at most only about 0.02 percent of tax liability.

The most pervasive changes are in the Internet-TAXSIM validation results, which are
now off a little bit because it would seem that Internet-TAXSIM contains the same bugs
as are fixed in this pull request.

This pull request resolves issue #873, which contains a more extensive discussion of
the code changes in this pull request.

@MattHJensen @feenberg @Amy-Xu @GoFroggyRun @zrisher @codykallen

---

You can view, comment on, or merge this pull request online at:

  #874

Commit Summary

• Rename function that calculates NIIT; fix modAGI.
• Eliminate negative NII values in NetInvIncTax function.
• Fix NIIT calculation logic; save small results differences.

File Changes

• M taxcalc/calculate.py (2)
• M taxcalc/comparison/reform_results.txt (2)
• M taxcalc/functions.py (13)
• M taxcalc/tests/pufcsv_agg_expect.txt (4)
• M taxcalc/tests/pufcsv_mtr_expect.txt (22)
• M taxcalc/validation/c13-reform-18_0.07.taxdiffs (3)
• M taxcalc/validation/c13-reform-19_0.05.taxdiffs (3)
• M taxcalc/validation/c13-reform-50_1.taxdiffs (3)
• M taxcalc/validation/c13-reform-75_500.taxdiffs (3)
• M taxcalc/validation/c13.taxdiffs (7)
• M taxcalc/validation/c14-reform-18_0.07.taxdiffs (3)
• M taxcalc/validation/c14-reform-19_0.05.taxdiffs (3)
• M taxcalc/validation/c14-reform-50_1.taxdiffs (3)
• M taxcalc/validation/c14-reform-75_500.taxdiffs (3)
• M taxcalc/validation/c14.taxdiffs (7)
• M taxcalc/validation/c15.taxdiffs (13)
• M taxcalc/validation/d13.taxdiffs (7)
• M taxcalc/validation/d14.taxdiffs (7)
• M taxcalc/validation/d15.taxdiffs (13)

Patch Links:

• https://github.com/open-source-economics/Tax-Calculator/pull/874.patch
• https://github.com/open-source-economics/Tax-Calculator/pull/874.diff

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[martinholmer]

Dan @feenberg said:

We will fix Internet TAXSIM this afternoon.

Thanks, Dan, for the speedy response.
Please notify when fixed, so I can redo the validation tests.

[feenberg]

On Wed, 24 Aug 2016, Martin Holmer wrote:

Dan @feenberg said:

  We will fix Internet TAXSIM this afternoon.

Thanks, Dan, for the speedy response.
Please notify when fixed, so I can redo the validation tests.

Ready now. Please report success/failure.

thanks for pointing this out.

dan

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